1. Field of the Invention
The present invention relates to a bipolar ion exchange membrane electrolytic cell.
2. Discussion of the Background
Ion exchange membrane electrolytic cells which have been widely used, are of a filter press (fastening) type electrolytic cell wherein, as shown in FIG. 4, a number of ion exchange membranes 20 and compartment frame units 21 are alternately arranged by interposing gaskets 22 (the thickness is drawn exaggeratedly), and the arranged elements are fastened from both sides by using a hydraulic press or the like. The electrolytic cell of this type is generally classified into a monopolar electrolytic cell of a parallel connection type and a bipolar electrolytic cell of a serial connection type, which are distinguishable from the difference in electrical connection.
In the bipolar ion exchange membrane electrolytic cell, as shown in FIG. 5, a compartment frame unit 21 is formed by connecting an anode compartment frame 30 and a cathode compartment frame 40 back to back. The anode compartment frame 30 for forming an anode compartment 31 comprises a back plate 32 and a meshed electrode plate 33 which is disposed substantially in parallel to the back plate 32 with a certain space to the back plate 32 wherein supporting members or ribs 34 are disposed between the back plate 32 and the anode plate 33 to maintain the above-mentioned space therebetween. Each of the supporting members 34 is provided with a plurality of openings through which electrode liquid or electrolyte can flow in the left and right directions in FIG. 5.
The construction of the cathode compartment frame 40 for providing a cathode compartment 41 is the same as that of the anode compartment frame 30. Namely, it comprises a back plate 42, a meshed cathode plate 43 and supporting members or ribs 44. The back plate 32 is connected integrally with the back plate 42 to form a partition wall for conducting an electric current. A peripheral edge portion of each of the back plates 32, 42 is bent and fixed to a hollow body or a square pipe 24.
FIG. 6 is a front view of the compartment frame unit 21, i.e., a view observed from the cathode side, wherein numeral 27 designates an inlet at the side of the cathode compartment frame 40 through which a cathode liquid or a catholyte is introduced. Numeral 28 designates an outlet for a catholyte and hydrogen gas. Similarly, an inlet 27a and an outlet 28a for an anode liquid are formed in the anode compartment frame 30.
In a case of an electrolytic cell for chlor-alkali manufacture, chlorine gas is generated in the anode compartment 31, and hydrogen gas is generated in the cathode compartment 41. Each gas is mixed with the liquid respectively to form a gas-liquid mixed phase stream. The stream goes up in each of the compartments to each gas-liquid separator 29 provided at the upper portion of the compartments where the gas-liquid mixture stream is separated into a gaseous phase and a liquid phase to be discharged from compartments through the outlets 28, 28a, respectively.
The gas-liquid separator may be such as disclosed in U.S. Pat. No. 5,225,060 in which a gas-liquid separating chamber is formed in a non-electrolysis area which is in an upper portion of each of the electrode plates, and at least one opening is formed at the bottom of the gas-liquid separating chamber so that the gas-liquid mixed phase stream passing upwardly in the compartments enters into the chamber through the opening.
Further, the gas-liquid separator may be such as disclosed in Japanese Examined Patent Publication No. 46191/1985 in which an L-shaped channel body is disposed in a electrolysis area to form a gas-liquid separating chamber, so that the gas-liquid mixed phase stream enters into the chamber from the electrode side and is discharged therethrough.
In such bipolar ion exchange membrane electrolytic cell, when the discharging of a gas-liquid mixed phase stream is not smoothly discharged, gas stagnates at an upper portion of the compartments. This causes fluctuation of pressure in the compartments; hence, voltage variation. Further, fluctuation of pressure in the compartments causes vibrations of adjacent ion exchange membranes and the ion exchange membranes frequently contact the electrode. Thus, the ion exchange membranes may deteriorate. Accordingly, it is necessary to separate gas quickly from liquid in the gas-liquid separators and to discharge them to the outside of the compartments. For this, the function of the gas-liquid separator is important.
In the gas-liquid separator formed in a non-current conductive, electrolysis area as disclosed in U.S. Pat. No. 5,225,060, gas easily stagnates near the opening formed at the bottom portion of a gas-liquid separating chamber, whereby the fluctuation of pressure in the compartment, the deterioration of ion exchange membrane and the variation of voltage in the compartment take place.
Further, in the gas-liquid separator formed in a current conductive area as disclosed in Japanese Examined Patent Publication No. 46191/1985, the gas-liquid mixed phase stream enters into a gas-liquid separating chamber through a gap or space between a electrode plate and gas-liquid separating chamber. Because the electrode is in a meshed form, gas easily stagnates between the electrode and the ion exchange membrane. Accordingly, the problems arise in that the pressure in the compartment fluctuates, the ion exchange membrane deteriorates and the voltage changes.